I propose to continue our efforts to grow crystals, suitable for X-ray diffraction studies, of calcium binding proteins in the EF-hand homolog family. We have already grown 0.1mm crystals, which diffract to 7 A spacing, of the modulator protein (MP) of adenylate cyclase. Most our effort will be focused on preparing MP from the brains of different animals in hopes of finding a MP which forms larger crystals. We will continue to try to crystallize whole troponin and the calcium binding protein of crayfish tail sarcoplasmic reticulum as we receive samples from collaborators. As new results on the heterogeneity and purification of tubulin become available, we will continue our attempts to crystallize it. We will soon complete our three dimensional difference Fourier synthesis study of the Tb3 ion, carp muscle calcium binding parvalbumin complex. BIBLIOGRAPHIC REFERENCES: kretsinger, R.H. "Why Does Calcium Play an Information Role Unique in Biological Systems?" In Metal-Ligand Interactions in Organic Chemistry and Biochemistry. Proceedings of the 9th Jerusalem Symposium on Quantum Chemistry and Biochemistry (1977). B. Pullman and N. Goldblum, eds. Reidel Publishing Co., Dordrecht, Holland. In press. Kretsinger, R.H. "Evolutionary Considerations of Calcium Pumping by Biological Membranes." In Ion Transport Across Membranes--the Proceedings of a Joint US-USSR Conference (1977). D.C. Tosteson, Y.A. Ovchinnikov and R. Latorre, eds. Raven Press, N.Y. In press.